[lkml]   [2013]   [Jul]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH V5 09/12] perf: make events stream always parsable
On 15/07/13 09:14, Adrian Hunter wrote:
> On 12/07/13 17:55, Peter Zijlstra wrote:
>> On Fri, Jul 12, 2013 at 03:56:01PM +0300, Adrian Hunter wrote:
>>>> There's events where this isn't a possible location; take PERF_RECORD_MMAP for
>>>> instance; the tail is the complete filename.
>>> PERF_RECORD_MMAP falls in the category I have called non-sample events.
>>> Those events are appended with an ID sample. perf tools parses the ID
>>> sample backwards from header.size. So the ID is at the last position
>>> relative to header.size
>> But why? Why make it different per PERF_RECORD type?
> There have always been two formats:
> 1. PERF_RECORD_SAMPLE as defined by perf_output_sample()
> 2. everything else as defined by __perf_event__output_id_sample()
> The two formats are not the same, and there is no reason for them to be.
> PERF_RECORD_SAMPLE is parsed forwards, so the ID is at the first position.
> ID samples are parsed backwards, so the ID is at the last position (i.e. the
> first position parsed).

If you want the ID at the first position in the ID sample, it is do-able.
It means perf tools will have to be changed to calculate the variable start
position of the ID sample, and then parse the ID sample forwards from there.
Please advise.

 \ /
  Last update: 2013-07-16 09:21    [W:0.092 / U:0.872 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site